1. Field of the Invention
This disclosure relates to a zoom lens and an image pickup apparatus having the zoom lens; the zoom lens is believed suitable for image pickup apparatuses using a solid state image pickup element such as digital still cameras, video cameras, monitoring cameras, broadcasting cameras and the like, or for image pickup apparatuses using silver halide film such as analog photography cameras and the like.
2. Description of the Related Art
In recent years, functions of image pickup apparatuses such as digital still cameras, video cameras, and the like using a solid image pickup element have improved and the size of such image pickup apparatuses has been reduced. A zoom lens used in these image pickup apparatuses is required to have a high magnification, wide viewing angle, a compact profile, and a favorable optical performance in the entire zoom range. To that end, a five-unit zoom lens comprising lens units having refractive powers of positive, negative, positive, negative, and positive from an object side to an image side in this order is known.
In the five-unit zoom lens, when the magnification of the zoom lens is increased, a focal length at a telephoto end is increased, and an on-axis chromatic aberration occurs often. In order to reduce the on-axis chromatic aberration, a zoom lens described in Japanese Patent Laid-Open No. 2012-220920 is formed of an anomalous dispersion glass material as a material of a positive lens included in the third lens unit.
In general, in order to obtain an image pickup optical system having a compact profile and a high magnification, the number of lenses which constitute each lens unit may be reduced while increasing a refracting power of each lens unit which constitutes part of the image pickup optical system. However, if the refracting power of the lens unit is increased, the refracting power of lens surfaces of the lenses which constitute the lens unit is increased, so that the lens thickness is increased in order to secure an edge thickness of the lens correspondingly. Consequently, a foremost lens diameter (effective diameter of the foremost lens) is increased, and hence a reduction in size of an optical system becomes difficult. In addition, by an increase in focal length at the telephoto end, chromatic aberration occurs often, so that a correction becomes difficult.